Sulfide Precipitation in Wastewater at Short Timescales

Abstract

Abatement of sulfides in sewer systems using iron salts is a widely used strategy. When dosing at the end of a pumping main, the reaction kinetics of sulfide precipitation becomes important. Traditionally the reaction has been assumed to be rapid or even instantaneous. This work shows that this is not the case for sulfide precipitation by ferric iron. Instead, the reaction time was found to be on a timescale where it must be considered when performing end-of-pipe treatment. For real wastewaters at pH 7, a stoichiometric ratio around 14 mol Fe(II) (mol S(−II)) −1 was obtained after 1.5 s, while the ratio dropped to about 5 mol Fe(II) (mol S(−II)) −1 after 30 s. Equilibrium calculations yielded a theoretic ratio of 2 mol Fe(II) (mol S(−II)) −1 , indicating that the process had not equilibrated within the span of the experiment. Correspondingly, the highest sulfide conversion only reached 60%. These findings differed significantly from what has been demonstrated in previous studies and what is attained from theoretical equilibrium conditions.

Gaseous Emissions from Wastewater Facilities

“…A 60% reduction in the peak odor concentration in the anaerobically digested dewatered cake was observed with 4% alum addition prior to dewatering. However, odor reduction in the dewatered sludge from WWTPs employing oxidation ditch processes was not observed.A work byKiilerich et al (2017) demonstrated that the precipitation of dissolved sulfide using ferrous iron was not instantaneous as previously assumed. The stoichiometric ratio was found to be 5-15 mol Fe per mol of sulfide at a reaction time of 1.5 s and fell to 4-6 mol at a reaction time of 30 s, indicating that the process had not reached equilibrium.…”

Microbial sulfate reduction by Desulfovibrio is an important source of hydrogen sulfide from a large swine finishing facility

“…The low-iron conditions of the swine waste point out to the possible solution to minimise sulfide emissions from the wastes by adding iron salts. The dosage of iron salts is a common and well-documented practice to reduce sulfide concentration in municipal sewage conveyance systems 6 , 31 . Ferrous iron (Fe 2+ ) reacts with sulfide (S 2− ) and precipitates it in the form of ferrous sulfides with low solubility.…”

The use of hay and sawdust to promote the removal of selenium and nitrate in coal mine drainage: A saturated up flow column experiment

“…This suggests another control for the effluent concentrations of Fe may have been present: co-precipitation with S 2as ferrous sulfide. The low solubility of this metal sulfide will result in the loss of reactants from solution (Kiilerich, et al, 2017). Pyrrhotite and troilite had saturation indices slightly above 0 for columns 1 and 5 in weeks 3 and 5 respectively, indicating a possible S consumption mechanism in the columns.…”